a home-made weapon used for CUTTING, not stabbing. a sharpened tooth-brush is not a shiv, that is a shank, which is used for stabbing.

guy 1:"i got cornered on my last day in prison, i was lucky i had my shiv!"
guy 2:"oh sweet! im going to jail soon, how do you make one?"
guy 1:"take a razor blade and a lighter in with you, then melt the blade to your toothbrush."